We and others have demostrated that the chromosomal translocations typical of Burkl++ lymphomas (BL) and other undifferentiated B-cell lymphomas (UBL), directly involve the c-myc oncogene locus. We have characterized the structural aspects of these translocations and identified different types of alterations of translocated c-myc alleles in different types of BL. Several questions critical for general understanding of the role of chromosomal translocations in malignancy remain open and will be addressed in the present research proposal. In particular, these questions include: 1) Mechanism(s) of chromosomal translocation. Our preliminary data by Southern blot analysis suggest that chromosomal translocations may result from mistakes in either the V-D-J joining (in endemic BL) or class switching (in sporadic BL) mechanisms of immunoglobulin genes and that these mistakes involve recombination with different sequences 5' or within the c-myc locus. These recombinations and their underlying mechanisms will be confirmed by cloning and nucleotide sequence analysis of the chromosomal breakpoints, ii) Mechanism of c-myc gene activation. We will test whether structural alterations detectable in translocated c-myc alleles are sufficient for c-myc activation. The sequences involved in c-myc regulation and activation will be identified by comparative analysis of BL mutants and in vitro constructed mutants in in vitro transformation assays. iii) Consequences of c-myc gene activation. We have preliminarily shown that high constitutive expression of transfected c-myc genes leads to an increase of the clonogenic potential of transformed B-cells. The genes involved in this phenomenon, i.e.the genes directly or indirectly regulated by c-myc, will be cloned from cDNA libraries of c-myc transfected cells and characterized. iv) Role of c-myc translocation in B-cell transformation in BL. A "recapitulation" of the genetic steps involved in BL pathogenesis will be attempted in vitro, by examing the individual or combined effects of translocated overexpressed c-myc genes, activated c-ras genes and other relevant oncogenes in primary human B-cells immortallized by Epstein-Barr Virus which represents another pathogenetic component of BL. Biological effects will be measured by studying morphology, growth factor dependency, clonagenic properties in semisolid media and tumorigenicity in nude mice.